Internet myth, only an IDIOT would walk into a possible firefight with an EMPTY weapon!
According to him, he wasn't in a firefights he was interrogating suspects when he used this technique and he had a ring of very well armed folks around him. He said even the hardest among them (those being interrogated) would start talking when they heard that sound.
That said, as nice as he is and though I consider him a friend, you're a lot braver than me if you want to call him and his contemporaries idiots.